Compact LWFA-Based Extreme Ultraviolet Free Electron Laser: Design Constraints

The combination of advanced high-power laser technology, new acceleration methods and achievements in undulator development offers the opportunity to build compact, high-brilliance free electron lasers driven by a laser wakefield accelerator. Here, we present a simulation study outlining the main requirements for the laser–plasma-based extreme ultraviolet free electron laser setup with the aim to reach saturation of the photon pulse energy in a single unit of a commercially available undulator with the deflection parameter K0 in the range of 1–1.5. A dedicated electron beam transport strategy that allows control of the electron beam slice parameters, including collective effects, required by the self-amplified spontaneous emission regime is proposed. Finally, a set of coherent photon radiation parameters achievable in the undulator section utilizing the best experimentally demonstrated electron beam parameters are analyzed. As a result, we demonstrate that the ultra-short, few-fs-level pulse of the photon radiation with the wavelength in the extreme ultraviolet range can be obtained with the peak brilliance of ∼7×1028 photons/pulse/mm2/mrad2/0.1%bw.

Quantum dissipative adaptation

Dissipative adaptation is a general thermodynamic mechanism that explains self-organization in a broad class of driven classical many-body systems. It establishes how the most likely (adapted) states of a system subjected to a given drive tend to be those following trajectories of highest work absorption, followed by dissipated heat to the reservoir. Here, we extend the dissipative adaptation phenomenon to the quantum realm. We employ a fully-quantized exactly solvable model, where the source of work on a three-level system is a single-photon pulse added to a zero-temperature infinite environment, a scenario that cannot be treated by the classical framework. We find a set of equalities relating adaptation likelihood, absorbed work, heat dissipation and variation of the informational entropy of the environment. Our proof of principle provides the starting point towards a quantum thermodynamics of driven self-organization.

Quantum Photovoltaic Cells Driven by Photon Pulses

We investigate the quantum thermodynamics of two quantum systems, a two-level system and a four-level quantum photocell, each driven by photon pulses as a quantum heat engine. We set these systems to be in thermal contact only with a cold reservoir while the heat (energy) source, conventionally given from a hot thermal reservoir, is supplied by a sequence of photon pulses. The dynamics of each system is governed by a coherent interaction due to photon pulses in terms of the Jaynes-Cummings Hamiltonian together with the system-bath interaction described by the Lindblad master equation. We calculate the thermodynamic quantities for the two-level system and the quantum photocell including the change in system energy, the power delivered by photon pulses, the power output to an external load, the heat dissipated to a cold bath, and the entropy production. We thereby demonstrate how a quantum photocell in the cold bath can operate as a continuum quantum heat engine with a sequence of photon pulses continuously applied. We specifically introduce the power efficiency of the quantum photocell in terms of the ratio of output power delivered to an external load with current and voltage to the input power delivered by the photon pulse. Our study indicates a possibility that a quantum system driven by external fields can act as an efficient quantum heat engine under non-equilibrium thermodynamics.

Methodology for calculating the average time of entry into synchronism of stations of the system of quantum key distribution with sequential polling of fiber-optic line sections with decreasing length by the graphic-analytical method

A method is proposed for calculating the average time of entry into synchronism of stations of the system of quantum key distribution (QKD) with sequential polling of sections of a fiber-optic communication line (FOCL) with decreasing length. A diagram of states and transitions for a sequential search for a photon pulse is constructed. Analytical expressions are obtained for finding the probability of detecting a photon pulse, the average number of steps for entry into synchronism of stations, the variance of the number of steps and the average time for entry into connection. It is noted that when the FOCL is divided into sections with decreasing length, the level of dark current pulses (DCP) significantly decreases from section to section. The latter allows to reduce the probability of false alarms of the photodetector. The analysis of the results obtained showed that the time of entry into synchronism for the proposed algorithm is 3 times less than the time required for entry into communication of stations in the case of an algorithm-analogue. The results obtained indicate the possibility of increasing the length of the FOCL while ensuring the value of the synchronization error probability at the level of 0.01.

Генерация когерентного рентгеновского излучения гармоник в однопроходном лазере на свободных электронах со сдвигом фаз электронов относительно фотонов

Theoretical study of the radiated FEL power and bunching is conducted in single-pass free electron laser (FEL) with repetitive shift of the photon pulse with respect to the electron bunch in between the sections of the undulator with field harmonics. Using the analytical calculations, the asymmetric elliptic and planar undulator fields are identified for the undulators to be able to reduce the fundamental tone and enhance the harmonic radiation. This effect is amplified by the phase shift kπ/n, k=2,4,6… of the electrons and photons between the undulator sections. This allows n-th FEL harmonic reach its peak power beyond the fundamental saturation FEL length. It is not possible to achieve in a common FEL due to fast increase of the energy spread, induced by the fundamental tone along FEL and its early saturation. The phenomenological model of the FEL is used for the analysis of the bunching coefficients and harmonic powers evolution in the FEL. The model describes the debunching between the undulator sections, where the phase shift is imposed, and accounts for the higher sensitivity to losses of the electron-photon interaction at high harmonic wavelengths. The losses are due to the beam energy spread and emittance, deviation off the axis, diffraction etc. Explicit expressions for the Bessel coefficients of the planar and elliptic undulators with field harmonics are obtained and analyzed. The combination of the undulator field harmonics is identified, which reduces the fundamental tone and enhances the 3rd and 5th UR harmonics as compared with the radiation from a planar undulator. We propose the use of these undulators in a FEL with the electron-photon phase shift, which increases high harmonic powers in X-ray band by ~100 times with respect to common FELs.